Complete second-order calculations of intensity parameters for one-photon and two-photon transitions of rare-earth ions in solids

Abstract

Biorthogonal perturbation methods originally developed for lanthanide crystal-field calculations are applied to 4f-4f electric dipole transition intensities for the system Pr³⁺-Cl^-. The results confirm earlier suggestions that ligand polarization contributions are crucial to understanding the relative signs of the intensity parameters. They also show that ‘covalent’ or ‘charge transfer’ excitations from occupied ligand states to 4f orbitals give significant contributions. Our calculations are also applied to two-photon absorption and electronic Raman scattering amplitudes. The major second-order contribution to these processes comes from excitations from 4f to 5d orbitals.